The present invention relates to a solid state imaging devices. More specifically, the present invention provides a novel structure for a solid state imaging device having the advantageous feature of reducing highlight image lag.
Conventionally, solid state imaging devices include photosensitive sections and signal charge transferring sections formed on a semiconductor substrate. The charge transferring sections are positioned adjacent to the photosensitive sections. The photosensitive sections must be made narrow, because it is necessary to position the signal charge transferring sections adjacent thereto. This causes the light utility factor and sensitivity of the the device to be low. Charges are generated in the semiconductor substrate except in photosensitive sections irradiated by a strong light, and these charges leak into the charge transferring sections. This phenomenon causes image smear.
To eliminate this drawback, there was developed a solid state imaging device having a silicon substrate including charge transferring sections and charge storage sections with a photoconductive layer provided on the silicon substrate. Such an arrangement is described in U.S. Pat. No. 4,360,821 which is incorporated herein by reference as if fully reproduced. This type of imaging device has high sensitivity, low blooming and low smear characteristics. Further, special sensitivity of the device can be controlled by selecting a particular type of photoconductive layer.
The known solid state imaging device having a photoconductive layer, as described above, has many advantages over imaging devices not having a photoconductive layer. However, it has a significant operational disadvantage. It exhibits the peculiarly undesirable phenomenon of image lag which occurs by virtue of the photoconductive layer itself. This phenomenon is particularly noticeable when a bright moving object is imaged, the image appearing to have a long tail which degrades image quality. This phenomenon is so called highlight image lag and to date this problem has not been dealt with adequately.